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I have a small closet (4x6) that I use to house my AV equipment (receiver/consoles/etc). This works great, but as the closet is in an upstairs room it gets quite warm in the summer. I would like to add a ventilation fan to that closet to exhaust some of the heat, but would prefer to avoid adding another exterior vent on the house.

I know venting bathroom/kitchen exhaust into attic is a bad plan due to moisture issues, but I am wondering if it would be OK in this case. The only air venting from the room would be warm dry air.

Any thoughts on just sticking a basic bathroom fan up their and venting into open space above the insulation (attic does have its own vents)?

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I'd have no concerns at all in doing this, assuming a well-ventilated attic. Be sure you have a functioning backflow preventer to keep cold air out in winter. Being more dense, it'll have a tendency to fall into the room.

  • Thanks, Considering the closet remains closed I am totally OK with a bit of cold air coming in (free cooling). Any issue with leaving a low CFM fan running 24/7 in there? Any particular models you would recommend? – Thildemar May 17 '16 at 17:57
  • No, and no. All bathroom-type fans seem to be cheap crap these days. Pick one with low sones (noise) and buy from a store with a good return policy for when it starts buzzing. – isherwood May 17 '16 at 18:00
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    I'd go to an HVAC shop and tell them what you're doing, have some idea of how many CFM you want and they can help you find a fan that'll run 24x7 for years. Keep an eye on the power usage, a 40W fan (probably more powerful than you need) running 24x7 for a year will use around $50 of power a year -- possibly more than the cost of the fan itself. – Johnny May 17 '16 at 18:06
  • Regarding your first comment, you won't want cold air streaming in when the fan is off (because it's not hot in the room). – isherwood May 17 '16 at 18:08
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    Probably overkill, but Panasonic make some fans that run very quietly/continuously (with a switched mode for when someone is actually using the bath, though that wouldn't apply to you, of course). They have optional sensors for humidity, which makes me wonder if they'd also have sensors for heat. – Aloysius Defenestrate May 18 '16 at 13:37
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Do not buy a bathroom fan, as they are generally rated to run no more than an hour or so at a time. You want a fan that's rated for continuous operation.

Do make sure your attic has sufficient ventilation area that you don't generate any back pressure. Similarly, figure out some way to get plenty of air into the closet, e.g. a screen panel in the door.

I would recommend getting the smallest fan with thermostatic control you can find, since the volume you're handling is pretty small. (or I suppose you could run the fan off a switched outlet on your A/V equipment so it's only running when the gear is live).

And as isherwood says, get a backflow preventer.

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